Announcement

Collapse
No announcement yet.

To de, or not to de: that is the question....

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • To de, or not to de: that is the question....

    A fun test on decoupling a woofer from the baffle with some surprising results. To be honest, I didn't expect to see much of a difference. At 30hz, it was a bit of an eye opener (See the video I'll be attaching right after this post). As I went up in frequency it changed again. By 40Hz, they were almost identical and by 50Hz, it had reversed and the hard-mounted woofer was showing the advantage. I'm thinking the result may change again if these baffles are mounted to a sealed box. Will try to find some time to get that done in the next few days and report back. May have a strobe light at my disposal in the near future also which should be pretty cool for seeing the results in a little different light (pun intended).

    Let start with the materials. I used EPDM foam across the board. Would other types of material be more suitable, maybe but this stuff seemed like a good starting place. Three EPDM materials involved, 1/8" sheet stock, 3/16"ID x 3/8" OD tubing, and 1/8" O-ring Cord stock. There were also some EPDM washers for the nuts on the back of the baffle but I ended up going a different route on that. Here are a few pics:

    Click image for larger version

Name:	DT1.jpg
Views:	1
Size:	414.8 KB
ID:	1373257


    In the following photo, you can see the tubing used to isolate the screws from the baffle.

    Click image for larger version

Name:	DT2.jpg
Views:	1
Size:	431.5 KB
ID:	1373258

    To prevent the frame of the woofer from touching the sides of the baffle, I used the 1/8" cord stock (installed in a groove cut with a saw cutter)

    Click image for larger version

Name:	DT3.jpg
Views:	1
Size:	413.6 KB
ID:	1373259

    The last piece on the front side of the baffle was a piece of 1/8" sheet stock cut as a gasket and cushion.

    Click image for larger version

Name:	DT4.jpg
Views:	1
Size:	547.0 KB
ID:	1373260

    The last piece of the puzzle. Tried flat EPDM washers but liked these panel grommets better. Seemed like there was more shock compression with these.

    Click image for larger version

Name:	DT5.jpg
Views:	1
Size:	428.3 KB
ID:	1373261

    Will post a video showing the results at 30Hz next.
    My "No-Name" CC Speaker
    Kerry's "Silverbacks"
    Ben's Synchaeta's for Mom
    The Archers
    Rick's "db" Desktop CBT Arrays
    The Gandalf's

  • #2
    My "No-Name" CC Speaker
    Kerry's "Silverbacks"
    Ben's Synchaeta's for Mom
    The Archers
    Rick's "db" Desktop CBT Arrays
    The Gandalf's

    Comment


    • #3
      Alright... that was frikkin cool! These things always remind me of the Jurassic Park water rumbling scene when the T-Rex shows up
      Voxel Down Firing with Dayton SA70
      Translam Subwoofers - The Jedi Mind Tricks
      The Super Bees - Garage 2 way
      SevenSixTwo - InDIYana 2018 Coax

      Comment


      • #4
        That is awesome!

        So many interesting questions...
        At 30Hz, obviously the wood is getting a lot less energy from the driver, presumably that's being absorbed by your decoupling material. Does that mean the woofer basket itself is physically moving slightly in opposition to the cone? What would that do to the acoustic energy output?
        Then at 50Hz, presumably the speed of the movement overcomes the compliance of your decoupling material so it's not effective, but why would it be worse than direct mount?
        And what does any of this do to the actual acoustic output / transfer function etc.?

        You've put me in a temporary existential "what does this all mean?" state
        Electronics engineer, woofer enthusiast, and musician.
        Wogg Music

        Comment


        • #5
          Perhaps an impedance sweep would give a bit more insight ?

          Comment


          • #6
            Next we'll be looking at the benefit of the Innovative Slice Cut Technique...

            Seriously though, there's some papers out there that had a little bit of discussion around them back in the UpperCut days, but no one really took them seriously because of the way the ideas were presented.

            Here's a few documents I found on the subject:

            http://www.linkwitzlab.com/Driver%20Decoupling.doc

            http://claudionegro.com/download/art...vibrations.pdf
            "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
            exactly a Fc 3K for both drivers, anybody can do it." -Xmax

            Comment


            • #7
              Cool stuff!
              Guess xmax's age.

              My guess: 15. His grammar is passable. His trolling is good.

              Comment


              • #8
                Originally posted by wogg View Post
                That is awesome!

                So many interesting questions...
                At 30Hz, obviously the wood is getting a lot less energy from the driver, presumably that's being absorbed by your decoupling material. Does that mean the woofer basket itself is physically moving slightly in opposition to the cone? What would that do to the acoustic energy output?
                Then at 50Hz, presumably the speed of the movement overcomes the compliance of your decoupling material so it's not effective, but why would it be worse than direct mount?
                And what does any of this do to the actual acoustic output / transfer function etc.?

                You've put me in a temporary existential "what does this all mean?" state

                ​I'm just as puzzled. Thought the results would stay linear but not the case. I'm planning to continue with the experiment but after mounting the baffle to an enclosure. This should make it a little easier on the drivers, I was pushing the heck out of them to get the water moving enough to see. Might also try a really fine sand in the cups to see if it's easier to move. If someone would just pony up an accelerometer, life could be so much easier. Sorry for putting you in the temporary state, hopefully we can prevent it from becoming permanent.
                My "No-Name" CC Speaker
                Kerry's "Silverbacks"
                Ben's Synchaeta's for Mom
                The Archers
                Rick's "db" Desktop CBT Arrays
                The Gandalf's

                Comment


                • #9
                  Originally posted by NyxOne View Post
                  Perhaps an impedance sweep would give a bit more insight ?
                  Agreed. After these baffles are mounted to boxes, I plan to take some measurements.
                  My "No-Name" CC Speaker
                  Kerry's "Silverbacks"
                  Ben's Synchaeta's for Mom
                  The Archers
                  Rick's "db" Desktop CBT Arrays
                  The Gandalf's

                  Comment


                  • #10
                    Originally posted by Kevin K. View Post
                    If someone would just pony up an accelerometer, life could be so much easier.
                    Just jam a condenser mic in the end of a stethoscope.
                    "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
                    exactly a Fc 3K for both drivers, anybody can do it." -Xmax

                    Comment


                    • #11
                      Originally posted by dcibel View Post
                      Next we'll be looking at the benefit of the Innovative Slice Cut Technique...

                      Seriously though, there's some papers out there that had a little bit of discussion around them back in the UpperCut days, but no one really took them seriously because of the way the ideas were presented.

                      Here's a few documents I found on the subject:

                      http://www.linkwitzlab.com/Driver%20Decoupling.doc

                      http://claudionegro.com/download/art...vibrations.pdf
                      ​Thanks for sharing. I was aware of Mr. Jones's work on this but hadn't seen this document. Interesting.
                      My "No-Name" CC Speaker
                      Kerry's "Silverbacks"
                      Ben's Synchaeta's for Mom
                      The Archers
                      Rick's "db" Desktop CBT Arrays
                      The Gandalf's

                      Comment


                      • #12
                        In your video, are both your test setups just resting on the table top? I'm assuming they are just sitting there and not clamped/bolted down. I would think that if you added a significant amount of mass to your test assemblies, the results would be closer to the same. If the transducer is rigidly coupled to the baffle, of course it's going to transfer more energy and the baffle will move more if it's not rigidly fixed or loaded with enough mass. When you begin to decouple it with something that gives, you won't transfer as much energy to the baffle and you've added loss to your system. Whether the loss of acoustic energy output is measurable/noticeable is up for debate. In your fixed woofer setup (at 30 Hz), you're transferring more energy in phase to your baffle test assembly and it's physically moving up and down more. With your decoupled setup, the resonant system you've created with your isolation material is allowing the frame of the woofer to move more and transfer less energy into your test baffle. Ideally, the way the woofer makes sound is by having the frame in a fixed physical position and moving only the cone to create pressure waves.

                        So, let's take a step back and look at the bigger picture... Presumably, you have a problem that the woofer is transferring energy into the baffle and the baffle is vibrating/resonating. What you're experimenting with is decoupling the woofer from the baffle so it does not transfer as much energy into the baffle and excite this resonance. IMO, this is similar to the guy who brags about how much power his car makes that allows him to do a burnout. As an engineer, I say that's cool that you make that much power, but it's actually a problem of lack of traction . In this case, instead of decoupling the woofer, why not address the problem of having resonant panels? Add extra bracing and/or increase the mass of the walls.

                        Just my 2 cents on this topic. I've had plans to get some accelerometers and run some experiments on box bracing, but I can't get the projects done I'm working on now

                        Comment


                        • #13
                          Originally posted by 1100xxben View Post
                          In your video, are both your test setups just resting on the table top? I'm assuming they are just sitting there and not clamped/bolted down. I would think that if you added a significant amount of mass to your test assemblies, the results would be closer to the same. If the transducer is rigidly coupled to the baffle, of course it's going to transfer more energy and the baffle will move more if it's not rigidly fixed or loaded with enough mass. When you begin to decouple it with something that gives, you won't transfer as much energy to the baffle and you've added loss to your system. Whether the loss of acoustic energy output is measurable/noticeable is up for debate. In your fixed woofer setup (at 30 Hz), you're transferring more energy in phase to your baffle test assembly and it's physically moving up and down more. With your decoupled setup, the resonant system you've created with your isolation material is allowing the frame of the woofer to move more and transfer less energy into your test baffle. Ideally, the way the woofer makes sound is by having the frame in a fixed physical position and moving only the cone to create pressure waves.

                          So, let's take a step back and look at the bigger picture... Presumably, you have a problem that the woofer is transferring energy into the baffle and the baffle is vibrating/resonating. What you're experimenting with is decoupling the woofer from the baffle so it does not transfer as much energy into the baffle and excite this resonance. IMO, this is similar to the guy who brags about how much power his car makes that allows him to do a burnout. As an engineer, I say that's cool that you make that much power, but it's actually a problem of lack of traction . In this case, instead of decoupling the woofer, why not address the problem of having resonant panels? Add extra bracing and/or increase the mass of the walls.

                          Just my 2 cents on this topic. I've had plans to get some accelerometers and run some experiments on box bracing, but I can't get the projects done I'm working on now
                          ​I agree with a lot of what you've said and realize not having the baffles anchored is certainly affecting the test. This was the reason I stated the next test would be done with them mounted to enclosures (significant amount of mass). Not to argue, but I've seen very few cabinets built with braces attached to the front baffle. As you know, there's not a lot of room left between a woofer and tweeter to add a brace which is why most builders focus their efforts of bracing on the sidewalls (larger panels) or other panels of the cabinet. With that being said, I suspect the results of the test to stay the same once the baffles are mounted in enclosures but that's just a guess on my part. There's much more to this than just the simple test I've performed here. Where is the energy going and how is it affecting the output of the driver. Hoping to be able to measure some of those things in the next round and I'm open to any suggestions you guys might have on test you would like to see.

                          For the record, the title of my thread is "To de(couple) or not to de(couple)" meaning I'm asking, not trying to convince anyone one way or the other, it's just a test spurned out of curiosity. Kind of hoping in the end there's no benefit because it sure makes things much easier to build without all of this stuff.
                          My "No-Name" CC Speaker
                          Kerry's "Silverbacks"
                          Ben's Synchaeta's for Mom
                          The Archers
                          Rick's "db" Desktop CBT Arrays
                          The Gandalf's

                          Comment


                          • #14
                            The less the driver moves due to adequate inertia in the launch platform, the better.
                            R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio

                            Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51


                            95% of Climate Models Agree: The Observations Must be Wrong
                            "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

                            Comment


                            • #15
                              Originally posted by Pete Schumacher View Post
                              The less the driver moves due to adequate inertia in the launch platform, the better.
                              So you are saying, that regardless of the transmission of vibrations from the driver to the baffle, that the driver frame should be anchored as solidly as possible. I can certainly understand, that a vibrating driver frame is not something anyone should want. Perhaps providing some anchor at the motor end can reduce the inertia at the baffle end as well, with the benefit of distributing the driver interia somewhere other than solely the front baffle?

                              In any case, the research I linked to above indicates that a large portion of the vibrations in cabinet walls are due to the fact that the drivers are coupled to the baffle, with the rest occurring from the internal cabinet SPL, meaning cabinet vibrations can be greatly reduced by decoupling the driver.I've not seen anything personally that indicates the effect this decoupling has on the driver output due to the frame not being as solidly anchored.
                              "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
                              exactly a Fc 3K for both drivers, anybody can do it." -Xmax

                              Comment

                              Working...
                              X